Props: youreslf, a big fellow student, a small fellow student, a skateboard.
1st Law: In motion, stay in motion; at rest, stay at rest.
Stand on skate board. If no one pushes, you don't move. If you are oushed, you move until some outside force -- like friction -- slows you to a stop.
2nd Law: Acceleration = Force/mass.
Big student stands on skateboard. Push. See how fast and far he/she travels. Small student stands on skateboard. Push. See how much faster, farther small student travels.
3rd Law: Action and opposite reaction.
Stand on skateboard. Push against small student standing on floor in front of you. Small student moves backward, so do you (in opposite direction).